1. Field of the Invention
The present invention relates to a cleaning device for removing toner left on an image carrier after the transfer of a toner image from the image carrier to a sheet or recording medium, and a copier, facsimile apparatus, printer or similar electrostatic image forming apparatus using the same.
2. Description of the Background Art
Today, there is an increasing demand for high-quality toner images available with an electrostatic image forming apparatus. Small size, spherical toner grains effectively enhance image quality, as recently reported in the imaging art. As for full-color images, gloss contributes a great deal to image quality, as also reported in the imaging art. Small size, spherical, dry toner grains with a narrow grain size distribution have been reported to implement high quality and high gloss. However, small size, spherical, dry toner grains have some problems left unsolved.
The most serious problem with the toner grains of the kind described is that it is difficult for a cleaning device to fully remove the toner grains left on an image carrier after image transfer, resulting in defective cleaning. Particularly, in a cleaning device of the type using a cleaning blade, toner gathers most densely at a nip between an image carrier and a cleaning blade during cleaning. As a result, a first toner layer strongly adhering to the image carrier and a second toner layer formed on the first layer slip on each other, so that the first layer remains on the image carrier.
Further, the blade of the cleaning device exerts a stress on wax dispersed in the toner grains. As a result, the wax comes out on the surfaces of the toner grains and deposit on the image carrier in the form of a film. The wax film reduces the frictional coefficient of the image carrier and therefore adhesion acting between the toner grains and the image carrier. In this condition, discharge is apt to transfer the toner grains from the image carrier to a sheet at a position short of the nip between them, resulting in an image with a dust-like defect.
In light of the above, a cleaning device with a cleaning roller or a cleaning brush has been proposed in various forms in the past. Japanese Patent Laid-Open Publication No. 2000-284664, for example, discloses a cleaning device including a collecting roller and a cleaning blade. In this cleaning device, the surface of a photoconductive drum is brought to a position spaced from the collecting roller by a preselected distance. At this position, the collecting roller collects normal toner grains left on the surface of the drum, allowing them to be used as recycled toner. Subsequently, the above surface of the drum is brought into contact with the cleaning blade. The cleaning blade removes toner grains also left on the drum, but reduced in size, for thereby distinguishing waste toner grains from the normal toner grains.
Japanese Patent Laid-Open Publication No. 5-188836 teaches a cleaning device of the type including a cleaning brush and a cleaning roller to each of which a particular voltage is applied. Toner collected by the cleaning brush from a photoconductive drum is transferred to the cleaning roller. A magnetic body is disposed in the cleaning roller below a horizontal plain containing the axis of the roller and spaced from the inner periphery of the roller by a preselected distance. The magnetic body may alternatively be implemented as a magnetic blade whose edge faces the cleaning roller. The magnetic blade removes toner from the cleaning roller being rotated. The above document describes that this type of developing device prevents image quality from being lowered and achieves a long life.
Further, Japanese Patent Laid-Open Publication No. 6-167912 proposes a cleaning device including a cleaning brush for collecting dust and a collecting roller for collecting the dust from the cleaning brush. When the cleaning device is not in operation, the cleaning brush is spaced from a portion to be cleaned and is rotated in a direction opposite to a direction assigned to cleaning. The document describes that this configuration prevents dust deposited on the cleaning brush from flying out of the cleaning device and extends the life of the cleaning brush.
However, in any one of the prior art cleaning devices described above, the ability of the cleaning roller or that of the cleaning brush falls due to aging although it may be desirable in the initial stage of use. More specifically, as the cleaning operation is repeated, the toner accumulates on the cleaning roller or fills interstices between the filaments of the cleaning brush to thereby reduce the diameter of the brush. In such a condition, the cleaning roller or the cleaning brush loses the expected cleaning ability.
Technologies relating to the present invention are also disclosed in, e.g., Japanese Patent Publication No. 56-30868 and Japanese Patent Laid-Open Publication Nos. 6-51579, 7-155222, 8-314349, 2000-75755, and 2000-292982.
It is an object of the present invention to provide a cleaning device capable of removing even small size, spherical, dry toner grains left on an image carrier after image transfer to thereby obviate defective cleaning, and an image forming apparatus using the same.
A cleaning device of the present invention is configured to remove toner left on an image carrier after the transfer of a toner image from the image carrier to a recording medium. A rotatable cleaning roller contacts the image carrier for removing the toner left on the image carrier. A rotatable brush roller is positioned upstream of the cleaning roller in the direction of rotation of the image carrier and rubs against the surface of the image carrier and that of the cleaning roller.
An image forming apparatus using the above cleaning device is also disclosed.